To install driver for Umax Astra 4400/4450 on Windows 7 you need to do the following.
1. Install VueScan from http://www.hamrick.com/
- It is only need it for C:\VueScan\scanner.inf with list of drivers
2. Manually install driver from Umax Astra 3400 - You can follow these instructions to install driver manually http://pcsupport.about.com/od/fixtheproblem/ht/update-drivers-windows-7.htm
3. Install Umax Astra 4400/4450 software (VistaScan) for Windows XP - Can be found at http://www.umax.com/download/index.jsp
5. Now you can scan using VistaScan (C:\VistaScan\Vista32.exe), but only the with flatbed option.
This solution is from Russian forum: http://forum.ixbt.com/topic.cgi?id=13:42660#7.